The present invention relates generally to a venting system which provides natural convection cooling. More particularly, the present invention relates to a venting system which expels combustion gases generated by a combustion process and in which the temperature of the outer wall sleeve of the venting system is reduced substantially.
The present invention is particularly useful in eliminating the need for a conventional chimney as found in newly constructed buildings, as well as in homes and other buildings that are being converted to utilize fossil fuels (i.e., oil, natural gas or propane) for heating and hot water making and which have not been constructed with chimneys. The use of the venting system of the present invention is advantageous when venting the products of combustion from a furnace, a heating unit, a boiler, a hot water heater or an incinerator through a combustible wall, since the temperature of the outer wall sleeve is substantially reduced from previously known systems.
In a typical building heating system, a furnace is located inside a building with a combustion chamber to which a flue pipe is connected so that the combustion gases generated in the combustion chamber of the furnace may flow through the flue pipe to a chimney up through the roof and be expelled into the atmosphere. Chimneys are made of brick and ceramic tile, or expensive insulated metal. Typical older style boilers or furnaces had high temperature flues--500.degree. F. and above, which required the use of a roof venting system. The more efficient modern; non-condensing appliances have combustion temperatures of about 350.degree. F.-400.degree. F. or below.
Such temperatures create problems as the combustion gases travel through the system for release into the atmosphere since the hot combustion gases raise the temperature of the flue pipe to such an extent that there is a risk of fire when the flue pipe passes through the combustible wall of the building. In addition, the heat generated by the combustion gases is also radiated to the exterior of the vent hood, thus creating a risk of burns to anyone touching the vent hood.
In the past, several systems have been constructed in which combustion air from the atmosphere is fed into a combustion chamber via an inlet duct. The flue products from the combustion chamber are expelled through another duct to the atmosphere. The combustion air inlet duct is generally located between the combustible wall or roof and the flue pipe so that the incoming combustion air serves to cool and reduce the wall or roof temperature. However, such devices do not use any specific cooling chambers and the air is not exhausted from the system by means of natural convection, as in the present invention. The only air that comes in through the inlet duct is used for combustion purposes.
Such systems differ from the system of the present invention in that the air in the vent hood is circulated between the flue pipe and the sleeve and is not later circulated to the combustion chamber. That air exits through the holes provided by the present invention which, in addition, causes the heated air to rise by a natural convection process and exit at the top of the vent. Typical of such prior art devices are the systems shown in the following: Stultz, U.S. Pat. No. 4,163,440; Ryder, U.S. Pat. No. 2,764,972; Hodges, U.S. Pat. No. 3,552,377; Little, U.S. Pat. No. 3,056,397; Jackson, U.S. Pat. No. 3,662,735; DeWerth, U.S. Pat. No. 3,435,816; Carlson, U.S. Pat. No. 3,211,079; Jackson, U.S. Pat. No. 4,262,608; and Winters et al., U.S. Pat. No. 3,994,280.
In another prior art system, as disclosed in U.S. Pat. No. 2,966,838 to Thompson, et al., a stagnant air gap between the flue pipe and the wall is used for cooling. However, because the heated air cannot escape from within the gap, hot air remains in the air gap and thus provides only limited cooling.
The present invention also provides natural convection cooling for the vent hood itself, which is attached to the flue pipe on the outside wall of the building. Various prior art designs for vent hoods are presently known. One such example is that disclosed in U.S. Pat. No. 3,056,397 to Little, in which the vent hood utilizes air inlet ducts at both the inner top portion and an inner bottom portion of the vent hood. Combustion gases are expelled at both an outer top portion and an outer bottom portion of the vent hood. Although the air inlet ducts cool the inner portion of the vent hood, the outer portion is not cooled to any great extent.
Another known design is disclosed in U.S. Pat. No. 2,998,764 to Bedell, et al., in which cool air is fed from the top inner portion and the bottom outer and inner portions of the vent hood and passes into a combustion chamber. Combustion gases are expelled through the top outer portion of the vent hood. However, Bedell, et al. does not disclose any method to cool the top outer portion of the vents through which the flue gases exit.